Federated States of Micronesia - Wikipedia, the free encyclopedia: "The island of Yap is notable for its stone money, large disks usually of calcite, up to 4 m (12 ft) in diameter, with a hole in the middle. The islanders know who owns which piece, but do not necessarily move them when ownership changes. There are five major types: Mmbul, Gaw, Ray, Yar, and Reng, this last being only 0.3 m (1 ft) in diameter. Their value is based on both size and history, many of them having been brought from other islands, as far as New Guinea, but most coming in ancient times from Palau. Approximately 6,500 of them are scattered around the island."